Beamforming Investigation of Dominant Counter-Rotating Open Rotor Tonal and Broadband Noise Sources

Phased array microphone measurements and beamforming technology have been applied in the investigation of counter-rotating open rotors in an attempt to better understand their noise sources. It has already been presented in the literature that the beamforming results of rotating coherent noise sources, typical tonal noise sources for counter-rotating open rotors, will be localized to their respective Mach radii rather than their true noise source locations. Building on these results, the present beamforming investigation provides an approach for identifying tonal and broadband noise sources of counter-rotating open rotors. The methods provide a means for localizing noise sources and identifying noise source mechanisms truly responsible for given components of tonal and broadband noise. Groups of interaction tones that can have the greatest impact on the sound field of counter-rotating open rotors are singled out, and the most dominant noise sources of broadband noise are determined.